1. Field of the Invention
The present invention relates to track searching on an optical disc drive (ODD), and more particularly, to a method and apparatus of canceling noise from a track cross signal generated when an optical spot (generated by a pickup) moves on an optical disc in the radial direction (i.e., it traverses tracks) so as to search for a desired track, a method of controlling an optical disc drive, an optical disc drive, and an optical disc reproducing apparatus.
2. Description of the Related Art
In general, a pickup of an optical disc drive (ODD) performs track searching on an optical disc in one of the following ways: (i) a direct seek control method and (ii) a course seek control method. In the direct seek control method, an optical spot reaches a desired track on an optical disc while searching all tracks through which the optical spot passes while moving in the radial direction. In the coarse seek control method, an optical spot moves directly to a predetermined point on an optical disc (i.e., near a desired track) without searching any track, and then reaches the desired track by searching adjacent tracks. With the coarse search control method, it is easy to search for a desired track, but the total access time is long. On the other hand, although the direct search control method is complicated, the total access time is short. For this reason, recently, the use of the direct seek control method has spread even for long-distance searches for tracks on a compact disc (CD), a digital versatile disc (DVD) drive, and so on.
FIG. 1 is a block diagram of a portion of a conventional optical disc drive. Referring to FIG. 1, the optical disc drive includes a hysteresis comparator 100, a noise removing apparatus 200 to cancel noise from a track cross signal, a controller 300, a drive 400, and a tracking actuator 500. As shown, the track cross signal is a signal read when a pickup (not shown) moves from a predetermined point on an optical disc in the radial direction, and then the optical spot transverses tracks on the optical disc. The track cross signal can be used in detecting the speed and position of the optical spot (pickup). The track cross signal is binarized by the hysteresis comparator 100 and a glitch noise is removed from the signal by the noise removing apparatus 200. Then, the controller 300 generates a control signal in response to the binarized track cross signal from which the noise was removed, and outputs the control signal to the drive 400. Next, the drive 400 drives the tracking actuator 500 in response to the control signal so as to move the pickup (not shown) to a desired point on the optical disc.
FIGS. 2A through 2C are timing diagrams for explaining a conventional method of canceling noise from a track cross signal. Referring to FIG. 2A, a track cross signal A contains noise and is detected by an optical disc. The hysteresis comparator 100 has upper and lower levels as reference levels used to binarize the track cross signal A, thereby obtaining a track zero cross signal B shown in FIG. 2B. However, the glitch noise is still contained in the track zero cross signal B. After one level of the track zero cross signal B changes into the other level, and then the changed level lasts for a predetermined time T, the noise removing apparatus 200 outputs a signal C shown in FIG. 2C. The signal C contains no glitch noise due to changes from the one level into the other level. The more the predetermined time value T is increased, the more clearly the glitch noise contained in a signal is removed. From FIGS. 2A through 2C, it is noted that the rising and falling edges of the signal C in which glitch noise was completely removed, are clearer than those of the signal B.
The time value T is a fixed value when changing the signal B to the signal C (i.e., removing glitch noise from the signal B) using the conventional noise removing apparatus 200. Therefore, in the event that a period of a track cross signal is shorter than two times of the predetermined time value T (i.e., 2 T), the level of the track cross signal changes before 2 T has passed. This makes it difficult to properly detect the signal C.
FIG. 3 is a waveform diagram of a track cross signal obtained by short-distance track searching at low speed. FIG. 4 is a waveform diagram of a track cross signal obtained by long-distance track searching at high speed. As shown in FIGS. 3 and 4, the frequency of the track cross signal obtained by the low-speed track searching is low, ranging from several KHz to tens of KHz. In contrast, the frequency of the track cross signal obtained by the high-speed track searching is very high, ranging from several KHz to hundreds of KHz. Accordingly, in order to obtain the signal C, the time value T must be set in consideration of the frequency of the track cross signal obtained by high-speeding track search.
Specifically, if the time value T is set to be high, it is possible to perfectly remove noise from a track cross signal obtained by the low-speed track searching. However, the frequency of the track cross signal, which is obtained by the high-speed track searching, becomes short and thus noise is not completely removed from the signal B. Specifically, the signal C is not properly detected. For this reason, the time value T is relatively short according to the frequency of the track cross signal during track searching at the high speed. However, in this case, the glitch noise cannot be completely removed from the signal B when searching a track at the low speed.